| brightness | <microscopy> The brightness of an extended luminous source is termed the intensity per unit area measured in candles per cm exp2. Also, the intensity of reflection, it may be measured in lamberts, one lambert equals 1 lumen/cm exp2. (05 Aug 1998) |
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| brightness difference threshold | The smallest difference that can be perceived as a difference in brightness. Synonym: light difference. (05 Mar 2000) |